Distributively banded reflector surface for producing contoured illumination intensity

ABSTRACT

A concave light reflector is shaped to have flat-sectioned radial bands on its inner surface extending radially outwardly and forwardly from the apex of the reflector. The bands are distributed circumferentially in an asymmetrical manner to provide a desired cross-sectional contour of illumination intensity, such as approximately rectangular for photographic projection purposes.

United States Patent [191 Downing et al.

[111 3,826,913 [451 Jul '30, 1974 DISTRIBUTIVELY BANDED REFLECTORSURFACE FOR PRODUCING CONTOURED ILLUMINATION INTENSITY Inventors: RobertD. Downing, Mentor;

Emmett H. Wiley, Chesterland, both of Ohio General Electric Company,Schenectady, N.Y.

Filed: May 24, 1973 Appl. No.: 363,509

Assignee:

US. Cl. 240/103 R, 240/4l.36

Int. Cl. F21v 7/09 Field of Search 240/l05, 41.36, 103 R, 240/ 103 CReferences Cited UNITED STATES PATENTS Balsillie IMO/41.36

Primary Examiner-Samuel S. Matthews Assistant Examiner-Russell E. Adams,Jr.

Attorney, Agent, or Firm-Norman C. Fulmer; Lawrence R. Kernpton; FrankL. Neuhauser ABSTRACT A concave light reflector is shaped to haveflatsectioned radial bands on its inner surface extending radiallyoutwardly and forwardly from the apex of the reflector. The bands aredistributed circumferentially in an asymmetrical manner to provide adesired crosssectional contour of illumination intensity, such asapproximately rectangular for photographic projection I purposes.

9 Claims, 3 Drawing Figures DISTRIBUTIVELY BANDED REFLECTOR SURFACE FORPRODUCING CONTOUREI) ILLUMINATION INTENSITY BACKGROUND OF THE INVENTIONThe invention is in the field of lighting devices, par ticularly thetype having a concave reflector for directing illumination in a givendirection.

Concave reflectors have been made in parabolic andellipticalconfigurations, and combinations and modifications of theseand other configurations, to produce desired patterns of projectedlight, such as a diverging light beam for broad-area illuminationpurposes or a converging light beam for photographic projection purposessuch as in projectors for movies or slide transparencies. Usually asmall light source of high intensity is positioned at the focal point ofthe reflector.

A typical concave reflector of circular cross section will project alight beam having circular contours of equal light intensity. However, arectangular type of equal light intensity contour is desired for certainpurposes, such as in diverging-beamphotographic lamps for illuminating ascene to be photographed and in converging-beam projection lamps formovie and slide projectors, Various ways have been devised for shaping aconcave reflector surface to produce a substantially rectangular or ovallight intensity configuration. For example,'U.S. Pat. No. 3,331,960 toElmer describes a concave reflector having a non-circular cross section;US. Pat. No. 3,423,582 to Elmer describes a concave reflector havingfour parabolic quadrants each with a different axis; U.S. Pat. No.3,428,800 to Levin-and Lemons describes a concave reflector having acontoured front edge; US. Pat. No. 3,588,493 to Nordquist describes aconcave reflector having four specially shaped sections or quadrants;and US. Pat. No. 3,720,460 to Wilkinson describes a concave reflectororiented to provide an offset angle of the focus axis.

SUMMARY OF THE INVENTION Objects of the invention are to provide a newand improved concave reflector for projecting a beam of light having asubstantially rectangular or oval crosssectional configuration of lightintensity,.and todo so with a reflector having a substantially circularcross section.

The invention comprises, briefly and in a preferred embodiment, aconcave light reflector which may have a generally circularcross-sectional shape, the inner surface thereof being shaped to providea plurality of radial bands extending radially outwardly and forwardlyfrom the apex of the reflector. The bands are distrib- FIG. 2 is a frontview of the assembly of FIG. 1; and

FIG. 3 is a front view of an alternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED. EMBODIMENT The general type of lamp andreflector assembly shown in the drawing is described in detail in US.Pat. No. 3,700,881 to Stanley Slomski, and comprises a concave reflectorll of molded glass provided with a multiple layer dichroiclight-reflective coating 12 on the inner surface thereof. The crosssection of the reflector is circular. A compact high intensity lamp 13is positioned within the reflector 11, and preferably com prises anelongated quartz envelope having a bulbous portion intermediate the endsthereof in which a high intensity are discharge is located at the focusof the reflector 11. A ceramic end cap 14 is attached to the rear of thereflector l1, and a pair of electrical connection wires l6, 17 extendfrom the end cap 14 and are attached to a connector plug 18. One of theconnector wires 16 is connected to an electrode (not shown) at the rearend of the lamp 13,'and the other connector wire 17 is connected to alead-in wire at the front end of the lamp 13, via an insulatedconnecting wire l9. A ceramic protective disc 20 is attached over thefront lead-in of the lamp. v

In accordance with the invention, a plurality of radial bands 21 areformed on the inner surface of the reflector 11, extending radiallyoutwardly and forwardly from the apex of the reflector, and distributedcircumferentially in an asymmetrical manner. Each-of the radial bands 21tapers to a point lying on acircumference rearwardly spaced from thefront edge of the reflector 11. The radial bands 21 may be made bymolding them simultaneously with molding the reflector, by suitablyshaping the reflector die or mold. The cross-section of each band, inplanes perpendicular to the optical axis of the reflector, preferably issubstantially flat, but may be inwardly curved toward the optical axis,or outwardly curved away from the optical axis with a radius utedcircumferentially in an asymmetrical manner to provide a desiredcross-sectional contour of illumination intensity. A substantiallyrectangular or ovallight intensity contour is obtained by providing acertain number of radial bands on each of a pair of opposed quadrants ofthe surface of the reflector, and a lesser number of wider radial bandson each of the other pair of opposed quadrants. In a modification,radial bands are provided on only one pair of opposed quadrants of thereflector surface.

BRIEF DESCRIPTION'OF THE DRAWING FIG. 1 is a perspective view of a lampand reflector assembly in accordance with a preferred embodiment of theinvention;

of curvature different from that of the circular main body of thereflector.

In the embodiment of FIGS. 1 and 2, the radial bands 21 at the sidequadrants of the reflector are relatively more numerous and narrowerthan the radial bands 21 at the top and bottom quadrants of thereflector. This asymmetrical arrangement of the radial banding producesa substantially rectangular or oval light intensity contour having alonger dimension horizontally than vertically, as indicated by thedashed-line representative light intensity contour curve 22 in FIG. 2.By suitably shaping the axial curvature of the reflector 11, thereflector will project forwardly a light beam from the lamp 13, ofeither a diverging or converging shape. The light intensity contour 22,on the scale shown, is representative of the light distribution patternof a diverging light beam at a lateral plane forwardly of the front edgeof the reflector 11. For a reflector shaped to form a converging lightbeam, the actual size of the light intensity contour curve 22 would besmaller than the front surface area of the reflector 11; such a lightintensity contour for a converging light beam is not shown in FIG. 2since it would tend to obfuscate the structural showing.

The substantially rectangular light beam pattern, as represented bycontour 22 in FIG. 2, provides a suitable light beam configuration foruse in illuminating a scene to be photographed, or for illumination ofdocuments in a document copying apparatus, in the case of a reflector 11producing a diverging light beam; and produces a suitably shaped lightbeam pattern in the case of a converging light beam reflector, forsuitably filling the aperture in a projector at which a movie film orslide transparency is positioned. The foregoing results are achievedwithout wasting light as would be the case of a circular light beampattern, where certain outer portions of the light beam would be wasted.

The invention functions due to the fact that each radial band reflects acertain amount of light sideways of itself, and the relatively widerradial bands in the vertical quadrants of the reflector reflectrelatively more light from the lamp l3 horizontally, than the amount oflight reflected in vertical directions by the relatively narrower radialbands in the horizontal quadrants. The radial bands 21 also tend tosoften the light beam, as described in the above-referenced U.S. Pat.No. 3,428,800 to Levin and Lemons.

The embodiment of FIG. 3 is the same as that of FIG. 2, except that theradial bands have been eliminated in the horizontal quadrants of thereflector 11, leaving the radial bands 21 only in the vertical reflectorquadrants. The asymmetrical banding arrangement of FIG. 3 produces alight beam having a substantially rectangular or oval light intensityconfiguration as is shown by the line 22 in FIG. 2, this being achieved,as described above, because the vertical radial bands 21 reflect some ofthe light from the lamp 13 sideways in a horizontal direction.

Various other asymmetrical radial banding configurations can be employedon reflectors of various kinds. For example, if the radial bands 21 wereomitted from the upper quadrant in FIG. 3, the light beam projected bythe reflector l 1 would be widened horizontally only in the lower partof the projected beam, such as might be useful for automobile headlightsor airplane lights. In any of the embodiments, the radial bands mayextend radially with respect to the apex without reaching either theapex or the front rim, or they may extend completely from the apex tothe front rim, or from the apex toward the front rim (as shown in thedrawing), or from the front rim toward the apex.

While preferred embodiments of the invention have been shown anddescribed, various other embodiments and modifications thereof willbecome apparent to persons skilled in the art and will fall within thescope of the invention as defined in the following claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A concave light reflector having a generally circular cross sectionand provided with radial bands on the inner surface thereof extendingradially outwardly and forwardly with respect to the apex of thereflector, wherein the improvement comprises an asymmetrical arrangementof said bands with respect to a circumference of said surface, wherebysaid reflector will projecta non-circular beam of light from a lamppositioned therein, each of said radial bands being separated from theadjacent bands along at least a substantial portion of the lengthsthereof, the reflector surface between adjacent bands being circularcross-section segments that are relatively wider at distances relativelyfarther from said apex of the reflector said radial bands having across-sectional curvature different from said separating surfaces.

2. A reflector as claimed in claim 1 in which a plurality of said radialbands are provided in each quadrant of the reflector, the radial bandsin one pair of opposed quadrants being symmetrical with respect to oneanother and asymmetrical with respect to the radial bands in the otherpair of opposed quadrants.

3. A reflector as claimed in claim 2 in which said one pair of opposedquadrants contains a different number of said radial bands than doessaid other pair of op posed quadrants.

4. A reflector as claimed in claim 2 in which said radial bands in saidone pair of opposed quadrants are relatively wider than the radial bandsin said other pair of opposed quadrants.

5. A reflector as claimed in claim 1 in which said radial bands areprovided in only one pair of opposed quadrants of said reflector.

6. A reflector as claimed in claim 5 in which the ra dial bands in saidpair of opposed quadrants are symmetrical with respect to one another.

7. A reflector as claimed in claim 1 in which the surface of each ofsaid radial bands is substantially flat in a plane perpendicular to theoptical axis of said reflector.

8. A reflector as claimed in claim 1, contoured to have a focus pointwithin the reflector, and in which each of said radial bands taperstoward a point in a direction toward the front edge of said reflectorsurface.

9. A reflector as claimed in claim 1 in which said radial bands arelocated in at least one of the quadrants of said reflector.

1. A concave light reflector having a generally circular cross sectionand provided with radial bands on the inner surface thereof extendingradially outwardly and forwardly with respect to the apex of thereflector, wherein the improvement comprises an asymmetrical arrangementof said bands with respect to a circumference of said surface, wherebysaid reflector will project a non-circular beam of light from a lamppositioned therein, each of said radial bands being separated from theadjacent bands along at least a substantial portion of the lengthsthereof, the reflector surface between adjacent bands being circularcross-section segments that are relatively wider at distances relativelyfarther from said apex of the reflector said radial bands having across-sectional curvature different from said separating surfaces.
 2. Areflector as claimed in claim 1 in which a plurality of said radialbands are provided in each quadrant of the reflector, the radial bandsin one pair of opposed quadrants being symmetrical with respect to oneanother and asymmetrical with respect to the radial bands in the otherpair of opposed quadrants.
 3. A reflector as claimed in claim 2 in whichsaid one pair of opposed quadrants contains a different number of saidradial bands than does said other pair of opposed quadrants.
 4. Areflector as claimed in claim 2 in which said radial bands in said onepair of opposed quadrants are relatively wider than the radial bands insaid other pair of opposed quadrants.
 5. A reflector as claimed in claim1 in which said radial bands are provided in only one pair of opposedquadrants of said reflector.
 6. A reflector as claimed in claim 5 inwhich the radial bands in said pair of opposed quadrants are symmetricalwith respect to one another.
 7. A reflector as claimed in claim 1 inwhich the surface of each of said radial bands is substantially flat ina plane perpendicular to the optical axis of said reflector.
 8. Areflector as claimed in claim 1, contoured to have a focus point withinthe reflector, and in which each of said radial bands tapers toward apoint in a direction toward the front edge of said reflector surface. 9.A reflector as claimed in claim 1 in which said radial bands are locatedin at least one of the quadrants of said reflector.